/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 *
 */

package java.lang;

import sun.misc.FloatingDecimal;
import java.util.Arrays;

/**
 * A mutable sequence of characters.
 * <p>
 * Implements a modifiable string. At any point in time it contains some
 * particular sequence of characters, but the length and content of the
 * sequence can be changed through certain method calls.
 *
 * <p>Unless otherwise noted, passing a {@code null} argument to a constructor
 * or method in this class will cause a {@link NullPointerException} to be
 * thrown.
 *
 * @author Michael McCloskey
 * @author Martin Buchholz
 * @author Ulf Zibis
 * @since 1.5
 */
abstract class AbstractStringBuilder implements Appendable, CharSequence {

  /**
   * The value is used for character storage.
   */
  char[] value;

  /**
   * The count is the number of characters used.
   */
  int count;

  /**
   * This no-arg constructor is necessary for serialization of subclasses.
   */
  AbstractStringBuilder() {
  }

  /**
   * Creates an AbstractStringBuilder of the specified capacity.
   */
  AbstractStringBuilder(int capacity) {
    value = new char[capacity];
  }

  /**
   * Returns the length (character count).
   *
   * @return the length of the sequence of characters currently represented by this object
   */
  @Override
  public int length() {
    return count;
  }

  /**
   * Returns the current capacity. The capacity is the amount of storage
   * available for newly inserted characters, beyond which an allocation
   * will occur.
   *
   * @return the current capacity
   */
  public int capacity() {
    return value.length;
  }

  /**
   * Ensures that the capacity is at least equal to the specified minimum.
   * If the current capacity is less than the argument, then a new internal
   * array is allocated with greater capacity. The new capacity is the
   * larger of:
   * <ul>
   * <li>The {@code minimumCapacity} argument.
   * <li>Twice the old capacity, plus {@code 2}.
   * </ul>
   * If the {@code minimumCapacity} argument is nonpositive, this
   * method takes no action and simply returns.
   * Note that subsequent operations on this object can reduce the
   * actual capacity below that requested here.
   *
   * @param minimumCapacity the minimum desired capacity.
   */
  public void ensureCapacity(int minimumCapacity) {
    if (minimumCapacity > 0) {
      ensureCapacityInternal(minimumCapacity);
    }
  }

  /**
   * This method has the same contract as ensureCapacity, but is
   * never synchronized.
   */
  private void ensureCapacityInternal(int minimumCapacity) {
    // overflow-conscious code
    if (minimumCapacity - value.length > 0) {
      expandCapacity(minimumCapacity);
    }
  }

  /**
   * This implements the expansion semantics of ensureCapacity with no
   * size check or synchronization.
   */
  void expandCapacity(int minimumCapacity) {
    int newCapacity = value.length * 2 + 2;
    if (newCapacity - minimumCapacity < 0) {
      newCapacity = minimumCapacity;
    }
    if (newCapacity < 0) {
      if (minimumCapacity < 0) // overflow
      {
        throw new OutOfMemoryError();
      }
      newCapacity = Integer.MAX_VALUE;
    }
    value = Arrays.copyOf(value, newCapacity);
  }

  /**
   * Attempts to reduce storage used for the character sequence.
   * If the buffer is larger than necessary to hold its current sequence of
   * characters, then it may be resized to become more space efficient.
   * Calling this method may, but is not required to, affect the value
   * returned by a subsequent call to the {@link #capacity()} method.
   */
  public void trimToSize() {
    if (count < value.length) {
      value = Arrays.copyOf(value, count);
    }
  }

  /**
   * Sets the length of the character sequence.
   * The sequence is changed to a new character sequence
   * whose length is specified by the argument. For every nonnegative
   * index <i>k</i> less than {@code newLength}, the character at
   * index <i>k</i> in the new character sequence is the same as the
   * character at index <i>k</i> in the old sequence if <i>k</i> is less
   * than the length of the old character sequence; otherwise, it is the
   * null character {@code '\u005Cu0000'}.
   *
   * In other words, if the {@code newLength} argument is less than
   * the current length, the length is changed to the specified length.
   * <p>
   * If the {@code newLength} argument is greater than or equal
   * to the current length, sufficient null characters
   * ({@code '\u005Cu0000'}) are appended so that
   * length becomes the {@code newLength} argument.
   * <p>
   * The {@code newLength} argument must be greater than or equal
   * to {@code 0}.
   *
   * @param newLength the new length
   * @throws IndexOutOfBoundsException if the {@code newLength} argument is negative.
   */
  public void setLength(int newLength) {
    if (newLength < 0) {
      throw new StringIndexOutOfBoundsException(newLength);
    }
    ensureCapacityInternal(newLength);

    if (count < newLength) {
      Arrays.fill(value, count, newLength, '\0');
    }

    count = newLength;
  }

  /**
   * Returns the {@code char} value in this sequence at the specified index.
   * The first {@code char} value is at index {@code 0}, the next at index
   * {@code 1}, and so on, as in array indexing.
   * <p>
   * The index argument must be greater than or equal to
   * {@code 0}, and less than the length of this sequence.
   *
   * <p>If the {@code char} value specified by the index is a
   * <a href="Character.html#unicode">surrogate</a>, the surrogate
   * value is returned.
   *
   * @param index the index of the desired {@code char} value.
   * @return the {@code char} value at the specified index.
   * @throws IndexOutOfBoundsException if {@code index} is negative or greater than or equal to
   * {@code length()}.
   */
  @Override
  public char charAt(int index) {
    if ((index < 0) || (index >= count)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    return value[index];
  }

  /**
   * Returns the character (Unicode code point) at the specified
   * index. The index refers to {@code char} values
   * (Unicode code units) and ranges from {@code 0} to
   * {@link #length()}{@code  - 1}.
   *
   * <p> If the {@code char} value specified at the given index
   * is in the high-surrogate range, the following index is less
   * than the length of this sequence, and the
   * {@code char} value at the following index is in the
   * low-surrogate range, then the supplementary code point
   * corresponding to this surrogate pair is returned. Otherwise,
   * the {@code char} value at the given index is returned.
   *
   * @param index the index to the {@code char} values
   * @return the code point value of the character at the {@code index}
   * @throws IndexOutOfBoundsException if the {@code index} argument is negative or not less than
   * the length of this sequence.
   */
  public int codePointAt(int index) {
    if ((index < 0) || (index >= count)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    return Character.codePointAtImpl(value, index, count);
  }

  /**
   * Returns the character (Unicode code point) before the specified
   * index. The index refers to {@code char} values
   * (Unicode code units) and ranges from {@code 1} to {@link
   * #length()}.
   *
   * <p> If the {@code char} value at {@code (index - 1)}
   * is in the low-surrogate range, {@code (index - 2)} is not
   * negative, and the {@code char} value at {@code (index -
   * 2)} is in the high-surrogate range, then the
   * supplementary code point value of the surrogate pair is
   * returned. If the {@code char} value at {@code index -
   * 1} is an unpaired low-surrogate or a high-surrogate, the
   * surrogate value is returned.
   *
   * @param index the index following the code point that should be returned
   * @return the Unicode code point value before the given index.
   * @throws IndexOutOfBoundsException if the {@code index} argument is less than 1 or greater than
   * the length of this sequence.
   */
  public int codePointBefore(int index) {
    int i = index - 1;
    if ((i < 0) || (i >= count)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    return Character.codePointBeforeImpl(value, index, 0);
  }

  /**
   * Returns the number of Unicode code points in the specified text
   * range of this sequence. The text range begins at the specified
   * {@code beginIndex} and extends to the {@code char} at
   * index {@code endIndex - 1}. Thus the length (in
   * {@code char}s) of the text range is
   * {@code endIndex-beginIndex}. Unpaired surrogates within
   * this sequence count as one code point each.
   *
   * @param beginIndex the index to the first {@code char} of the text range.
   * @param endIndex the index after the last {@code char} of the text range.
   * @return the number of Unicode code points in the specified text range
   * @throws IndexOutOfBoundsException if the {@code beginIndex} is negative, or {@code endIndex} is
   * larger than the length of this sequence, or {@code beginIndex} is larger than {@code
   * endIndex}.
   */
  public int codePointCount(int beginIndex, int endIndex) {
    if (beginIndex < 0 || endIndex > count || beginIndex > endIndex) {
      throw new IndexOutOfBoundsException();
    }
    return Character.codePointCountImpl(value, beginIndex, endIndex - beginIndex);
  }

  /**
   * Returns the index within this sequence that is offset from the
   * given {@code index} by {@code codePointOffset} code
   * points. Unpaired surrogates within the text range given by
   * {@code index} and {@code codePointOffset} count as
   * one code point each.
   *
   * @param index the index to be offset
   * @param codePointOffset the offset in code points
   * @return the index within this sequence
   * @throws IndexOutOfBoundsException if {@code index} is negative or larger then the length of
   * this sequence, or if {@code codePointOffset} is positive and the subsequence starting with
   * {@code index} has fewer than {@code codePointOffset} code points, or if {@code codePointOffset}
   * is negative and the subsequence before {@code index} has fewer than the absolute value of
   * {@code codePointOffset} code points.
   */
  public int offsetByCodePoints(int index, int codePointOffset) {
    if (index < 0 || index > count) {
      throw new IndexOutOfBoundsException();
    }
    return Character.offsetByCodePointsImpl(value, 0, count,
        index, codePointOffset);
  }

  /**
   * Characters are copied from this sequence into the
   * destination character array {@code dst}. The first character to
   * be copied is at index {@code srcBegin}; the last character to
   * be copied is at index {@code srcEnd-1}. The total number of
   * characters to be copied is {@code srcEnd-srcBegin}. The
   * characters are copied into the subarray of {@code dst} starting
   * at index {@code dstBegin} and ending at index:
   * <pre>{@code
   * dstbegin + (srcEnd-srcBegin) - 1
   * }</pre>
   *
   * @param srcBegin start copying at this offset.
   * @param srcEnd stop copying at this offset.
   * @param dst the array to copy the data into.
   * @param dstBegin offset into {@code dst}.
   * @throws IndexOutOfBoundsException if any of the following is true: <ul> <li>{@code srcBegin} is
   * negative <li>{@code dstBegin} is negative <li>the {@code srcBegin} argument is greater than the
   * {@code srcEnd} argument. <li>{@code srcEnd} is greater than {@code this.length()}. <li>{@code
   * dstBegin+srcEnd-srcBegin} is greater than {@code dst.length} </ul>
   */
  public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) {
    if (srcBegin < 0) {
      throw new StringIndexOutOfBoundsException(srcBegin);
    }
    if ((srcEnd < 0) || (srcEnd > count)) {
      throw new StringIndexOutOfBoundsException(srcEnd);
    }
    if (srcBegin > srcEnd) {
      throw new StringIndexOutOfBoundsException("srcBegin > srcEnd");
    }
    System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
  }

  /**
   * The character at the specified index is set to {@code ch}. This
   * sequence is altered to represent a new character sequence that is
   * identical to the old character sequence, except that it contains the
   * character {@code ch} at position {@code index}.
   * <p>
   * The index argument must be greater than or equal to
   * {@code 0}, and less than the length of this sequence.
   *
   * @param index the index of the character to modify.
   * @param ch the new character.
   * @throws IndexOutOfBoundsException if {@code index} is negative or greater than or equal to
   * {@code length()}.
   */
  public void setCharAt(int index, char ch) {
    if ((index < 0) || (index >= count)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    value[index] = ch;
  }

  /**
   * Appends the string representation of the {@code Object} argument.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(Object)},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param obj an {@code Object}.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(Object obj) {
    return append(String.valueOf(obj));
  }

  /**
   * Appends the specified string to this character sequence.
   * <p>
   * The characters of the {@code String} argument are appended, in
   * order, increasing the length of this sequence by the length of the
   * argument. If {@code str} is {@code null}, then the four
   * characters {@code "null"} are appended.
   * <p>
   * Let <i>n</i> be the length of this character sequence just prior to
   * execution of the {@code append} method. Then the character at
   * index <i>k</i> in the new character sequence is equal to the character
   * at index <i>k</i> in the old character sequence, if <i>k</i> is less
   * than <i>n</i>; otherwise, it is equal to the character at index
   * <i>k-n</i> in the argument {@code str}.
   *
   * @param str a string.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(String str) {
    if (str == null) {
      return appendNull();
    }
    int len = str.length();
    ensureCapacityInternal(count + len);
    str.getChars(0, len, value, count);
    count += len;
    return this;
  }

  // Documentation in subclasses because of synchro difference
  public AbstractStringBuilder append(StringBuffer sb) {
    if (sb == null) {
      return appendNull();
    }
    int len = sb.length();
    ensureCapacityInternal(count + len);
    sb.getChars(0, len, value, count);
    count += len;
    return this;
  }

  /**
   * @since 1.8
   */
  AbstractStringBuilder append(AbstractStringBuilder asb) {
    if (asb == null) {
      return appendNull();
    }
    int len = asb.length();
    ensureCapacityInternal(count + len);
    asb.getChars(0, len, value, count);
    count += len;
    return this;
  }

  // Documentation in subclasses because of synchro difference
  @Override
  public AbstractStringBuilder append(CharSequence s) {
    if (s == null) {
      return appendNull();
    }
    if (s instanceof String) {
      return this.append((String) s);
    }
    if (s instanceof AbstractStringBuilder) {
      return this.append((AbstractStringBuilder) s);
    }

    return this.append(s, 0, s.length());
  }

  private AbstractStringBuilder appendNull() {
    int c = count;
    ensureCapacityInternal(c + 4);
    final char[] value = this.value;
    value[c++] = 'n';
    value[c++] = 'u';
    value[c++] = 'l';
    value[c++] = 'l';
    count = c;
    return this;
  }

  /**
   * Appends a subsequence of the specified {@code CharSequence} to this
   * sequence.
   * <p>
   * Characters of the argument {@code s}, starting at
   * index {@code start}, are appended, in order, to the contents of
   * this sequence up to the (exclusive) index {@code end}. The length
   * of this sequence is increased by the value of {@code end - start}.
   * <p>
   * Let <i>n</i> be the length of this character sequence just prior to
   * execution of the {@code append} method. Then the character at
   * index <i>k</i> in this character sequence becomes equal to the
   * character at index <i>k</i> in this sequence, if <i>k</i> is less than
   * <i>n</i>; otherwise, it is equal to the character at index
   * <i>k+start-n</i> in the argument {@code s}.
   * <p>
   * If {@code s} is {@code null}, then this method appends
   * characters as if the s parameter was a sequence containing the four
   * characters {@code "null"}.
   *
   * @param s the sequence to append.
   * @param start the starting index of the subsequence to be appended.
   * @param end the end index of the subsequence to be appended.
   * @return a reference to this object.
   * @throws IndexOutOfBoundsException if {@code start} is negative, or {@code start} is greater
   * than {@code end} or {@code end} is greater than {@code s.length()}
   */
  @Override
  public AbstractStringBuilder append(CharSequence s, int start, int end) {
    if (s == null) {
      s = "null";
    }
    if ((start < 0) || (start > end) || (end > s.length())) {
      throw new IndexOutOfBoundsException(
          "start " + start + ", end " + end + ", s.length() "
              + s.length());
    }
    int len = end - start;
    ensureCapacityInternal(count + len);
    for (int i = start, j = count; i < end; i++, j++) {
      value[j] = s.charAt(i);
    }
    count += len;
    return this;
  }

  /**
   * Appends the string representation of the {@code char} array
   * argument to this sequence.
   * <p>
   * The characters of the array argument are appended, in order, to
   * the contents of this sequence. The length of this sequence
   * increases by the length of the argument.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(char[])},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param str the characters to be appended.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(char[] str) {
    int len = str.length;
    ensureCapacityInternal(count + len);
    System.arraycopy(str, 0, value, count, len);
    count += len;
    return this;
  }

  /**
   * Appends the string representation of a subarray of the
   * {@code char} array argument to this sequence.
   * <p>
   * Characters of the {@code char} array {@code str}, starting at
   * index {@code offset}, are appended, in order, to the contents
   * of this sequence. The length of this sequence increases
   * by the value of {@code len}.
   * <p>
   * The overall effect is exactly as if the arguments were converted
   * to a string by the method {@link String#valueOf(char[], int, int)},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param str the characters to be appended.
   * @param offset the index of the first {@code char} to append.
   * @param len the number of {@code char}s to append.
   * @return a reference to this object.
   * @throws IndexOutOfBoundsException if {@code offset < 0} or {@code len < 0} or {@code offset+len
   * > str.length}
   */
  public AbstractStringBuilder append(char str[], int offset, int len) {
    if (len > 0)                // let arraycopy report AIOOBE for len < 0
    {
      ensureCapacityInternal(count + len);
    }
    System.arraycopy(str, offset, value, count, len);
    count += len;
    return this;
  }

  /**
   * Appends the string representation of the {@code boolean}
   * argument to the sequence.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(boolean)},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param b a {@code boolean}.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(boolean b) {
    if (b) {
      ensureCapacityInternal(count + 4);
      value[count++] = 't';
      value[count++] = 'r';
      value[count++] = 'u';
      value[count++] = 'e';
    } else {
      ensureCapacityInternal(count + 5);
      value[count++] = 'f';
      value[count++] = 'a';
      value[count++] = 'l';
      value[count++] = 's';
      value[count++] = 'e';
    }
    return this;
  }

  /**
   * Appends the string representation of the {@code char}
   * argument to this sequence.
   * <p>
   * The argument is appended to the contents of this sequence.
   * The length of this sequence increases by {@code 1}.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(char)},
   * and the character in that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param c a {@code char}.
   * @return a reference to this object.
   */
  @Override
  public AbstractStringBuilder append(char c) {
    ensureCapacityInternal(count + 1);
    value[count++] = c;
    return this;
  }

  /**
   * Appends the string representation of the {@code int}
   * argument to this sequence.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(int)},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param i an {@code int}.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(int i) {
    if (i == Integer.MIN_VALUE) {
      append("-2147483648");
      return this;
    }
    int appendedLength = (i < 0) ? Integer.stringSize(-i) + 1
        : Integer.stringSize(i);
    int spaceNeeded = count + appendedLength;
    ensureCapacityInternal(spaceNeeded);
    Integer.getChars(i, spaceNeeded, value);
    count = spaceNeeded;
    return this;
  }

  /**
   * Appends the string representation of the {@code long}
   * argument to this sequence.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(long)},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param l a {@code long}.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(long l) {
    if (l == Long.MIN_VALUE) {
      append("-9223372036854775808");
      return this;
    }
    int appendedLength = (l < 0) ? Long.stringSize(-l) + 1
        : Long.stringSize(l);
    int spaceNeeded = count + appendedLength;
    ensureCapacityInternal(spaceNeeded);
    Long.getChars(l, spaceNeeded, value);
    count = spaceNeeded;
    return this;
  }

  /**
   * Appends the string representation of the {@code float}
   * argument to this sequence.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(float)},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param f a {@code float}.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(float f) {
    FloatingDecimal.appendTo(f, this);
    return this;
  }

  /**
   * Appends the string representation of the {@code double}
   * argument to this sequence.
   * <p>
   * The overall effect is exactly as if the argument were converted
   * to a string by the method {@link String#valueOf(double)},
   * and the characters of that string were then
   * {@link #append(String) appended} to this character sequence.
   *
   * @param d a {@code double}.
   * @return a reference to this object.
   */
  public AbstractStringBuilder append(double d) {
    FloatingDecimal.appendTo(d, this);
    return this;
  }

  /**
   * Removes the characters in a substring of this sequence.
   * The substring begins at the specified {@code start} and extends to
   * the character at index {@code end - 1} or to the end of the
   * sequence if no such character exists. If
   * {@code start} is equal to {@code end}, no changes are made.
   *
   * @param start The beginning index, inclusive.
   * @param end The ending index, exclusive.
   * @return This object.
   * @throws StringIndexOutOfBoundsException if {@code start} is negative, greater than {@code
   * length()}, or greater than {@code end}.
   */
  public AbstractStringBuilder delete(int start, int end) {
    if (start < 0) {
      throw new StringIndexOutOfBoundsException(start);
    }
    if (end > count) {
      end = count;
    }
    if (start > end) {
      throw new StringIndexOutOfBoundsException();
    }
    int len = end - start;
    if (len > 0) {
      System.arraycopy(value, start + len, value, start, count - end);
      count -= len;
    }
    return this;
  }

  /**
   * Appends the string representation of the {@code codePoint}
   * argument to this sequence.
   *
   * <p> The argument is appended to the contents of this sequence.
   * The length of this sequence increases by
   * {@link Character#charCount(int) Character.charCount(codePoint)}.
   *
   * <p> The overall effect is exactly as if the argument were
   * converted to a {@code char} array by the method
   * {@link Character#toChars(int)} and the character in that array
   * were then {@link #append(char[]) appended} to this character
   * sequence.
   *
   * @param codePoint a Unicode code point
   * @return a reference to this object.
   * @throws IllegalArgumentException if the specified {@code codePoint} isn't a valid Unicode code
   * point
   */
  public AbstractStringBuilder appendCodePoint(int codePoint) {
    final int count = this.count;

    if (Character.isBmpCodePoint(codePoint)) {
      ensureCapacityInternal(count + 1);
      value[count] = (char) codePoint;
      this.count = count + 1;
    } else if (Character.isValidCodePoint(codePoint)) {
      ensureCapacityInternal(count + 2);
      Character.toSurrogates(codePoint, value, count);
      this.count = count + 2;
    } else {
      throw new IllegalArgumentException();
    }
    return this;
  }

  /**
   * Removes the {@code char} at the specified position in this
   * sequence. This sequence is shortened by one {@code char}.
   *
   * <p>Note: If the character at the given index is a supplementary
   * character, this method does not remove the entire character. If
   * correct handling of supplementary characters is required,
   * determine the number of {@code char}s to remove by calling
   * {@code Character.charCount(thisSequence.codePointAt(index))},
   * where {@code thisSequence} is this sequence.
   *
   * @param index Index of {@code char} to remove
   * @return This object.
   * @throws StringIndexOutOfBoundsException if the {@code index} is negative or greater than or
   * equal to {@code length()}.
   */
  public AbstractStringBuilder deleteCharAt(int index) {
    if ((index < 0) || (index >= count)) {
      throw new StringIndexOutOfBoundsException(index);
    }
    System.arraycopy(value, index + 1, value, index, count - index - 1);
    count--;
    return this;
  }

  /**
   * Replaces the characters in a substring of this sequence
   * with characters in the specified {@code String}. The substring
   * begins at the specified {@code start} and extends to the character
   * at index {@code end - 1} or to the end of the
   * sequence if no such character exists. First the
   * characters in the substring are removed and then the specified
   * {@code String} is inserted at {@code start}. (This
   * sequence will be lengthened to accommodate the
   * specified String if necessary.)
   *
   * @param start The beginning index, inclusive.
   * @param end The ending index, exclusive.
   * @param str String that will replace previous contents.
   * @return This object.
   * @throws StringIndexOutOfBoundsException if {@code start} is negative, greater than {@code
   * length()}, or greater than {@code end}.
   */
  public AbstractStringBuilder replace(int start, int end, String str) {
    if (start < 0) {
      throw new StringIndexOutOfBoundsException(start);
    }
    if (start > count) {
      throw new StringIndexOutOfBoundsException("start > length()");
    }
    if (start > end) {
      throw new StringIndexOutOfBoundsException("start > end");
    }

    if (end > count) {
      end = count;
    }
    int len = str.length();
    int newCount = count + len - (end - start);
    ensureCapacityInternal(newCount);

    System.arraycopy(value, end, value, start + len, count - end);
    str.getChars(value, start);
    count = newCount;
    return this;
  }

  /**
   * Returns a new {@code String} that contains a subsequence of
   * characters currently contained in this character sequence. The
   * substring begins at the specified index and extends to the end of
   * this sequence.
   *
   * @param start The beginning index, inclusive.
   * @return The new string.
   * @throws StringIndexOutOfBoundsException if {@code start} is less than zero, or greater than the
   * length of this object.
   */
  public String substring(int start) {
    return substring(start, count);
  }

  /**
   * Returns a new character sequence that is a subsequence of this sequence.
   *
   * <p> An invocation of this method of the form
   *
   * <pre>{@code
   * sb.subSequence(begin,&nbsp;end)}</pre>
   *
   * behaves in exactly the same way as the invocation
   *
   * <pre>{@code
   * sb.substring(begin,&nbsp;end)}</pre>
   *
   * This method is provided so that this class can
   * implement the {@link CharSequence} interface.
   *
   * @param start the start index, inclusive.
   * @param end the end index, exclusive.
   * @return the specified subsequence.
   * @throws IndexOutOfBoundsException if {@code start} or {@code end} are negative, if {@code end}
   * is greater than {@code length()}, or if {@code start} is greater than {@code end}
   * @spec JSR-51
   */
  @Override
  public CharSequence subSequence(int start, int end) {
    return substring(start, end);
  }

  /**
   * Returns a new {@code String} that contains a subsequence of
   * characters currently contained in this sequence. The
   * substring begins at the specified {@code start} and
   * extends to the character at index {@code end - 1}.
   *
   * @param start The beginning index, inclusive.
   * @param end The ending index, exclusive.
   * @return The new string.
   * @throws StringIndexOutOfBoundsException if {@code start} or {@code end} are negative or greater
   * than {@code length()}, or {@code start} is greater than {@code end}.
   */
  public String substring(int start, int end) {
    if (start < 0) {
      throw new StringIndexOutOfBoundsException(start);
    }
    if (end > count) {
      throw new StringIndexOutOfBoundsException(end);
    }
    if (start > end) {
      throw new StringIndexOutOfBoundsException(end - start);
    }
    return new String(value, start, end - start);
  }

  /**
   * Inserts the string representation of a subarray of the {@code str}
   * array argument into this sequence. The subarray begins at the
   * specified {@code offset} and extends {@code len} {@code char}s.
   * The characters of the subarray are inserted into this sequence at
   * the position indicated by {@code index}. The length of this
   * sequence increases by {@code len} {@code char}s.
   *
   * @param index position at which to insert subarray.
   * @param str A {@code char} array.
   * @param offset the index of the first {@code char} in subarray to be inserted.
   * @param len the number of {@code char}s in the subarray to be inserted.
   * @return This object
   * @throws StringIndexOutOfBoundsException if {@code index} is negative or greater than {@code
   * length()}, or {@code offset} or {@code len} are negative, or {@code (offset+len)} is greater
   * than {@code str.length}.
   */
  public AbstractStringBuilder insert(int index, char[] str, int offset,
      int len) {
    if ((index < 0) || (index > length())) {
      throw new StringIndexOutOfBoundsException(index);
    }
    if ((offset < 0) || (len < 0) || (offset > str.length - len)) {
      throw new StringIndexOutOfBoundsException(
          "offset " + offset + ", len " + len + ", str.length "
              + str.length);
    }
    ensureCapacityInternal(count + len);
    System.arraycopy(value, index, value, index + len, count - index);
    System.arraycopy(str, offset, value, index, len);
    count += len;
    return this;
  }

  /**
   * Inserts the string representation of the {@code Object}
   * argument into this character sequence.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(Object)},
   * and the characters of that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param obj an {@code Object}.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, Object obj) {
    return insert(offset, String.valueOf(obj));
  }

  /**
   * Inserts the string into this character sequence.
   * <p>
   * The characters of the {@code String} argument are inserted, in
   * order, into this sequence at the indicated offset, moving up any
   * characters originally above that position and increasing the length
   * of this sequence by the length of the argument. If
   * {@code str} is {@code null}, then the four characters
   * {@code "null"} are inserted into this sequence.
   * <p>
   * The character at index <i>k</i> in the new character sequence is
   * equal to:
   * <ul>
   * <li>the character at index <i>k</i> in the old character sequence, if
   * <i>k</i> is less than {@code offset}
   * <li>the character at index <i>k</i>{@code -offset} in the
   * argument {@code str}, if <i>k</i> is not less than
   * {@code offset} but is less than {@code offset+str.length()}
   * <li>the character at index <i>k</i>{@code -str.length()} in the
   * old character sequence, if <i>k</i> is not less than
   * {@code offset+str.length()}
   * </ul><p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param str a string.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, String str) {
    if ((offset < 0) || (offset > length())) {
      throw new StringIndexOutOfBoundsException(offset);
    }
    if (str == null) {
      str = "null";
    }
    int len = str.length();
    ensureCapacityInternal(count + len);
    System.arraycopy(value, offset, value, offset + len, count - offset);
    str.getChars(value, offset);
    count += len;
    return this;
  }

  /**
   * Inserts the string representation of the {@code char} array
   * argument into this sequence.
   * <p>
   * The characters of the array argument are inserted into the
   * contents of this sequence at the position indicated by
   * {@code offset}. The length of this sequence increases by
   * the length of the argument.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(char[])},
   * and the characters of that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param str a character array.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, char[] str) {
    if ((offset < 0) || (offset > length())) {
      throw new StringIndexOutOfBoundsException(offset);
    }
    int len = str.length;
    ensureCapacityInternal(count + len);
    System.arraycopy(value, offset, value, offset + len, count - offset);
    System.arraycopy(str, 0, value, offset, len);
    count += len;
    return this;
  }

  /**
   * Inserts the specified {@code CharSequence} into this sequence.
   * <p>
   * The characters of the {@code CharSequence} argument are inserted,
   * in order, into this sequence at the indicated offset, moving up
   * any characters originally above that position and increasing the length
   * of this sequence by the length of the argument s.
   * <p>
   * The result of this method is exactly the same as if it were an
   * invocation of this object's
   * {@link #insert(int, CharSequence, int, int) insert}(dstOffset, s, 0, s.length())
   * method.
   *
   * <p>If {@code s} is {@code null}, then the four characters
   * {@code "null"} are inserted into this sequence.
   *
   * @param dstOffset the offset.
   * @param s the sequence to be inserted
   * @return a reference to this object.
   * @throws IndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int dstOffset, CharSequence s) {
    if (s == null) {
      s = "null";
    }
    if (s instanceof String) {
      return this.insert(dstOffset, (String) s);
    }
    return this.insert(dstOffset, s, 0, s.length());
  }

  /**
   * Inserts a subsequence of the specified {@code CharSequence} into
   * this sequence.
   * <p>
   * The subsequence of the argument {@code s} specified by
   * {@code start} and {@code end} are inserted,
   * in order, into this sequence at the specified destination offset, moving
   * up any characters originally above that position. The length of this
   * sequence is increased by {@code end - start}.
   * <p>
   * The character at index <i>k</i> in this sequence becomes equal to:
   * <ul>
   * <li>the character at index <i>k</i> in this sequence, if
   * <i>k</i> is less than {@code dstOffset}
   * <li>the character at index <i>k</i>{@code +start-dstOffset} in
   * the argument {@code s}, if <i>k</i> is greater than or equal to
   * {@code dstOffset} but is less than {@code dstOffset+end-start}
   * <li>the character at index <i>k</i>{@code -(end-start)} in this
   * sequence, if <i>k</i> is greater than or equal to
   * {@code dstOffset+end-start}
   * </ul><p>
   * The {@code dstOffset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   * <p>The start argument must be nonnegative, and not greater than
   * {@code end}.
   * <p>The end argument must be greater than or equal to
   * {@code start}, and less than or equal to the length of s.
   *
   * <p>If {@code s} is {@code null}, then this method inserts
   * characters as if the s parameter was a sequence containing the four
   * characters {@code "null"}.
   *
   * @param dstOffset the offset in this sequence.
   * @param s the sequence to be inserted.
   * @param start the starting index of the subsequence to be inserted.
   * @param end the end index of the subsequence to be inserted.
   * @return a reference to this object.
   * @throws IndexOutOfBoundsException if {@code dstOffset} is negative or greater than {@code
   * this.length()}, or {@code start} or {@code end} are negative, or {@code start} is greater than
   * {@code end} or {@code end} is greater than {@code s.length()}
   */
  public AbstractStringBuilder insert(int dstOffset, CharSequence s,
      int start, int end) {
    if (s == null) {
      s = "null";
    }
    if ((dstOffset < 0) || (dstOffset > this.length())) {
      throw new IndexOutOfBoundsException("dstOffset " + dstOffset);
    }
    if ((start < 0) || (end < 0) || (start > end) || (end > s.length())) {
      throw new IndexOutOfBoundsException(
          "start " + start + ", end " + end + ", s.length() "
              + s.length());
    }
    int len = end - start;
    ensureCapacityInternal(count + len);
    System.arraycopy(value, dstOffset, value, dstOffset + len,
        count - dstOffset);
    for (int i = start; i < end; i++) {
      value[dstOffset++] = s.charAt(i);
    }
    count += len;
    return this;
  }

  /**
   * Inserts the string representation of the {@code boolean}
   * argument into this sequence.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(boolean)},
   * and the characters of that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param b a {@code boolean}.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, boolean b) {
    return insert(offset, String.valueOf(b));
  }

  /**
   * Inserts the string representation of the {@code char}
   * argument into this sequence.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(char)},
   * and the character in that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param c a {@code char}.
   * @return a reference to this object.
   * @throws IndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, char c) {
    ensureCapacityInternal(count + 1);
    System.arraycopy(value, offset, value, offset + 1, count - offset);
    value[offset] = c;
    count += 1;
    return this;
  }

  /**
   * Inserts the string representation of the second {@code int}
   * argument into this sequence.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(int)},
   * and the characters of that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param i an {@code int}.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, int i) {
    return insert(offset, String.valueOf(i));
  }

  /**
   * Inserts the string representation of the {@code long}
   * argument into this sequence.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(long)},
   * and the characters of that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param l a {@code long}.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, long l) {
    return insert(offset, String.valueOf(l));
  }

  /**
   * Inserts the string representation of the {@code float}
   * argument into this sequence.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(float)},
   * and the characters of that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param f a {@code float}.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, float f) {
    return insert(offset, String.valueOf(f));
  }

  /**
   * Inserts the string representation of the {@code double}
   * argument into this sequence.
   * <p>
   * The overall effect is exactly as if the second argument were
   * converted to a string by the method {@link String#valueOf(double)},
   * and the characters of that string were then
   * {@link #insert(int, String) inserted} into this character
   * sequence at the indicated offset.
   * <p>
   * The {@code offset} argument must be greater than or equal to
   * {@code 0}, and less than or equal to the {@linkplain #length() length}
   * of this sequence.
   *
   * @param offset the offset.
   * @param d a {@code double}.
   * @return a reference to this object.
   * @throws StringIndexOutOfBoundsException if the offset is invalid.
   */
  public AbstractStringBuilder insert(int offset, double d) {
    return insert(offset, String.valueOf(d));
  }

  /**
   * Returns the index within this string of the first occurrence of the
   * specified substring. The integer returned is the smallest value
   * <i>k</i> such that:
   * <pre>{@code
   * this.toString().startsWith(str, <i>k</i>)
   * }</pre>
   * is {@code true}.
   *
   * @param str any string.
   * @return if the string argument occurs as a substring within this object, then the index of the
   * first character of the first such substring is returned; if it does not occur as a substring,
   * {@code -1} is returned.
   */
  public int indexOf(String str) {
    return indexOf(str, 0);
  }

  /**
   * Returns the index within this string of the first occurrence of the
   * specified substring, starting at the specified index.  The integer
   * returned is the smallest value {@code k} for which:
   * <pre>{@code
   *     k >= Math.min(fromIndex, this.length()) &&
   *                   this.toString().startsWith(str, k)
   * }</pre>
   * If no such value of <i>k</i> exists, then -1 is returned.
   *
   * @param str the substring for which to search.
   * @param fromIndex the index from which to start the search.
   * @return the index within this string of the first occurrence of the specified substring,
   * starting at the specified index.
   */
  public int indexOf(String str, int fromIndex) {
    return String.indexOf(value, 0, count, str, fromIndex);
  }

  /**
   * Returns the index within this string of the rightmost occurrence
   * of the specified substring.  The rightmost empty string "" is
   * considered to occur at the index value {@code this.length()}.
   * The returned index is the largest value <i>k</i> such that
   * <pre>{@code
   * this.toString().startsWith(str, k)
   * }</pre>
   * is true.
   *
   * @param str the substring to search for.
   * @return if the string argument occurs one or more times as a substring within this object, then
   * the index of the first character of the last such substring is returned. If it does not occur
   * as a substring, {@code -1} is returned.
   */
  public int lastIndexOf(String str) {
    return lastIndexOf(str, count);
  }

  /**
   * Returns the index within this string of the last occurrence of the
   * specified substring. The integer returned is the largest value <i>k</i>
   * such that:
   * <pre>{@code
   *     k <= Math.min(fromIndex, this.length()) &&
   *                   this.toString().startsWith(str, k)
   * }</pre>
   * If no such value of <i>k</i> exists, then -1 is returned.
   *
   * @param str the substring to search for.
   * @param fromIndex the index to start the search from.
   * @return the index within this sequence of the last occurrence of the specified substring.
   */
  public int lastIndexOf(String str, int fromIndex) {
    return String.lastIndexOf(value, 0, count, str, fromIndex);
  }

  /**
   * Causes this character sequence to be replaced by the reverse of
   * the sequence. If there are any surrogate pairs included in the
   * sequence, these are treated as single characters for the
   * reverse operation. Thus, the order of the high-low surrogates
   * is never reversed.
   *
   * Let <i>n</i> be the character length of this character sequence
   * (not the length in {@code char} values) just prior to
   * execution of the {@code reverse} method. Then the
   * character at index <i>k</i> in the new character sequence is
   * equal to the character at index <i>n-k-1</i> in the old
   * character sequence.
   *
   * <p>Note that the reverse operation may result in producing
   * surrogate pairs that were unpaired low-surrogates and
   * high-surrogates before the operation. For example, reversing
   * "\u005CuDC00\u005CuD800" produces "\u005CuD800\u005CuDC00" which is
   * a valid surrogate pair.
   *
   * @return a reference to this object.
   */
  public AbstractStringBuilder reverse() {
    boolean hasSurrogates = false;
    int n = count - 1;
    for (int j = (n - 1) >> 1; j >= 0; j--) {
      int k = n - j;
      char cj = value[j];
      char ck = value[k];
      value[j] = ck;
      value[k] = cj;
      if (Character.isSurrogate(cj) ||
          Character.isSurrogate(ck)) {
        hasSurrogates = true;
      }
    }
    if (hasSurrogates) {
      reverseAllValidSurrogatePairs();
    }
    return this;
  }

  /**
   * Outlined helper method for reverse()
   */
  private void reverseAllValidSurrogatePairs() {
    for (int i = 0; i < count - 1; i++) {
      char c2 = value[i];
      if (Character.isLowSurrogate(c2)) {
        char c1 = value[i + 1];
        if (Character.isHighSurrogate(c1)) {
          value[i++] = c1;
          value[i] = c2;
        }
      }
    }
  }

  /**
   * Returns a string representing the data in this sequence.
   * A new {@code String} object is allocated and initialized to
   * contain the character sequence currently represented by this
   * object. This {@code String} is then returned. Subsequent
   * changes to this sequence do not affect the contents of the
   * {@code String}.
   *
   * @return a string representation of this sequence of characters.
   */
  @Override
  public abstract String toString();

  /**
   * Needed by {@code String} for the contentEquals method.
   */
  final char[] getValue() {
    return value;
  }

}
